The present invention relates generally to the field of digital image devices. In particular, the invention relates to external aperturing of digital micromirror devices that may be implemented in, for example, digital projectors.
A typical architecture for a digital projector having a digital micromirror device (DMD) is illustrated in FIG. 1. A typical projector arrangement 100 includes a light source portion 110, a projection portion 120 and an image processing portion 130. The light source portion 110 includes a light source and one or more lenses directing the light to the image processing portion 130. The processed image is then directed from the image processing portion 130 through the projection portion 120 to, for example, a screen. The projection portion also includes one or more lenses to direct and/or focus the image onto the screen.
FIG. 2 illustrates the image processing portion 130 in greater detail. The key component of the image processing portion 130 is a DMD 140 which processes the light into pixels of the image. DMD's are well known to those skilled in the art and do not require further discussion for purposes of this application. A DMD cover plate 150 is provided on the reflective surface of the DMD 140. In a telecentric architecture, a total internal reflection (TIR) prism arrangement 160 is provided in close proximity to the DMD 140. The light from the light source portion 110 is reflected from an internal surface of the TIR prism arrangement 160 to an active region 142 of the DMD 140, which directs the processed image through the TIR prism arrangement 160.
FIG. 3 is a front view of the DMD 140. The active area 142 of the DMD 140 is positioned in a central region. The active area 142 includes reflective surfaces to reflect incoming light to form an image. In order to more precisely define the image, a non-reflective perimeter 144 is formed around the active region to absorb any overfill of incoming light outside the active area. In many instances, the width of the non-reflective perimeter is limited by the manufacturer, in part, due to cost considerations. As a result, the on-screen extinction ratio, or contrast, may be adversely affected. Further, certain optical artifacts reflected by portions of the DMD outside the non-reflective perimeter, such as reflected light from bond leads 146, may be relayed to the screen.
Configuring the non-reflective region at the plane of the active area 140 can be costly. It is desirable to achieve simple and economical systems and methods for enhancing the contrast of the image in such digital projectors.